This is a renewal application for continued support of a comprehensive program dealing with the structure and metabolism of heterogeneous nuclear RNA and messenger RNA. We have shown that hnRNA and mRNA possess a ribonucleoprotein structure. Recently we have mapped some of the interactions of specific hnRNP proteins with defined RNA sequences, such as poly(A) and double-stranded regions (transcripts of inverted repeat DNA sequences). A poly(A)-specific protein ("P74") has been identified in hnRNP particles from both HeLa cells and Dictyostelium (Kish and Pederson, 1975; Firtel and Pederson, 1975) as well as in polyribosomal messenger RNP (Kish and Pederson, 1976). This specific RNA-protein interaction is the subject to further the suggestion that the binding site for P74 is an oligo(U) sequence base-paired with poly(a) (Kish and Pederson, 1977a). Other projects will focus on the supramolecular organization of hnRNP, which we believe consists of repeating subunit structure not unlike the nucleosome organization of chromatin. We shall also continue to investigate the ribonucleoprotein structure of double-stranded sequences in hnRNA with particular emphasis on a ribonuclease activity we find complexed with dsRNA and which may be an important component of the hnRNA processing machinery. We will also pursue the characterization of hnRNP. Finally, we propose a comprehensive program aimed at mapping the ribonucleoprotein structure of both viral RNA genomes (myxovirused, rhabdoviruses) and viral messenger RNA (picornaviruses).